It produces no greenhouse gases, utilizes uranium fuel, which is abundant worldwide, and can contribute to hydrogen production.

Waste management and nuclear materials controls are essential for its deployment, but both are achievable.

Deployment of advanced water reactor systems is not far away -- several designs already exist.

For the most promising of these, simpler designs and modern construction techniques have meant lower costs, while protective systems, which rely only on gravity for activation and operation have enhanced their safety.

In the next 15 years, at least 60 of these plants will be in use worldwide, according to the United Nations International Atomic Energy Agency.

Smaller -- though less powerful -- water-cooled and gas-cooled designs, which further exploit laws of physics to promote safety, will also begin to be used.

The gas reactors use unique microscopic fuel particles in which the uranium is encased in layers of pyrolitic graphite and silicon carbide to contain radioactive products.

The water design houses all vital components in its single reactor vessel. These smaller modular type reactors promise safer, competitively priced electricity, particularly for countries with smaller but growing electrical grids.

Used fuel from all these reactors will be destined for underground geologic disposal sites to become available in the United States, France and Scandinavia.

However, the portion of used fuel needing geologic disposal can be reduced to a small fraction by the development of cost effective recycling processes -- processes that must be highly efficient to contain radioactive elements to avoid creation of burdensome waste streams.

Such processes will be investigated intensively in the coming decades.

If the development is successful we can contemplate reactors operating in a closed fuel cycle -- reactors fueled with natural uranium, which recycle their spent fuel and require discharge of just five percent of their spent fuel to geologic storage.

A third type of reactor, the fast neutron liquid metal or perhaps a gas cooled type, will be required to fully utilize this closed fuel cycle.

In 20 years' time, they will be well on the drawing board, and likely to be in use a few decades later.

These reactors will eliminate any fuel resource constraint by allowing breeding of new fuel from their natural uranium charge when the economically recoverable world uranium supplies dwindle-likely not before the next century.

While much hope rests on nuclear energy as a solution to the world's energy problems, and while advanced water reactor systems are set to contribute to this, the promise of smaller light-water reactors (LWR) and gas reactors remains to be proven -- and of course creating suitable recycling schemes is a big challenge.

Doubts aside, both have a big payoff if they are successful and both are worth trying hard to achieve.

The ability to generate a multi million-fold increase of electricity from uranium, compared to an equal mass of coal or oil, will forever inspire the vision of abundant energy to the world from nuclear technology.